This invention relates to triglycerides having stability with lapse of time, and a method for stabilization thereof. More particularly, it relates to triglycerides having stability with lapse of time, such as properties of preventing hydrolysis and stabilizing the melting point, and the method for stabilization thereof.
Triglycerides, that is oils and fats, have so far been produced from naturally found materials, and are used in a variety of applications, such as in industrial usage or for foods, cosmetics and medicines. In recent years, synthetic triglycerides obtained by esterification of fatty acids and glycerin, or so-called synthetic lipids, have attracted attention with respect to their physical and chemical properties, and are employed as a base for cosmetics and medicines.
However, triglycerides are known to undergo hydrolysis with lapse of time, as evidenced by the hydrolysis of edible oils and fats (see "J. Japan Oil Chem. Soc.", vol.26, page 150 (1977)), deterioration of shortening, butter and margarine (vol. 16, page 13, (1967), ibid) and deterioration of hardened coconut oil (vol.16, page 506, (1967), ibid). Such hydrolysis of triglycerides with lapse of time occurs not only in natural oils and fats, but also in synthetic oils and fats, with the result that free fatty acids are formed to give rise to deficiencies such as disagreeable smells and degradation in quality. For these reasons, methods have been proposed in recent years for preventing hydrolysis of triglycerides for realizing stability of the triglycerides with lapse of time, such as, for example, methods of random-interesterification ("J. Japan Oil Chem. Soc.", vol.18, page 730 (1969)), addition of liquid oils (vol.19, page 397, (1970), ibid) or addition of surfactants (vol.21, page 888, (1972), ibid).
However, although the hydrolysis of triglycerides with lapse of time is ascribable to polymorphism specific to the triglycerides, the situation is that account has not been taken sufficiently of the polymorphism in the aforementioned conventional methods for preventing the hydrolysis. Therefore, these conventional methods for preventing the hydrolysis have a drawback that, while they have some effects on natural oils and fats, they do not have sufficient effects on synthetic oils and fats. With the addition of the liquid oils or surfactants, it is necessary to add considerable amounts of these agents, since the addition of small amounts gives only limited effects. Hence, the properties natural to the triglycerides are impaired such that the triglycerides cannot be used as a base for cosmetics or medicines. Hence, the situation is that, while there is a strong demand for triglycerides free from hydrolysis with lapse of time and having superior stability with lapse of time, the triglycerides fully meeting these requirements have not yet been produced.